这是c++斑竹aogun的回答
在定时之前，先调用QueryPerformanceFrequency()函数获得时钟频率， 然后在事件发生前后分别调用QueryPerformanceCounter()函数，通过计数之差及时钟频率，计算出事件经 历的精确时间
下面的例子是测试int i = 0及上下语句执行间的时间间隔，时间单位为秒，以double类型为精度
例子：
程序代码:
#include <iostream>
#include <Windows.h>
using namespace std;
void main(void)
{
LONGLONG begin_time;
LONGLONG end_time;
double time_fre;
double time_elapsed;
LARGE_INTEGER litmp;
QueryPerformanceFrequency(&litmp);
time_fre = (double)litmp.QuadPart;
QueryPerformanceCounter((LARGE_INTEGER *)&begin_time);
int i = 0; //测试int i = 0及上下语句执行间的时间间隔，秒为单位
QueryPerformanceCounter((LARGE_INTEGER *)&end_time);
time_elapsed = (end_time - begin_time) / time_fre;
cout.precision(20);
cout<<"time elapsed:"<<time_elapsed<<endl;
}
